The present invention concerns an improved apparatus for isolating a pressure-sensitive device from blood flowing in an extracorporeal blood system and for transmitting the blood pressure to the pressure sensing device.
In a typical extracorporeal blood system, such as dialysis or oxygenation, for example, blood is pumped from a patient through an administration set which contains a bubble trap, through the mass transfer device (such as the dialyzer or the oxygenator), through another administration set which contains a bubble trap and back to the patient. The blood pressures in the line are typically monitored using one or more pressure-sensitive transducers. The transducers are isolated from the blood flow line by means of an isolating device which may be coupled between the blood flow line and the pressure-sensitive transducer. The isolating device must be operable to protect the transducer, to provide a sterile barrier and to transmit the blood pressure to the transducer.
One type of isolating and blood pressure transmitting device is disclosed in Gangemi U.S. Pat. No. 4,077,882, issued Mar. 7, 1978. I have discovered an isolating device that is superior in construction and operation with respect to the device disclosed in the Gangemi U.S. Patent, in that the present invention is simpler in construction and thus provides manufacturing advantages, has a construction which requires less membrane displacement thus resulting in less head pressure losses and a more accurate pressure transmission. As a safety feature, construction of the apparatus of the present invention is such that unequal pressure on either side of the membrane diaphragm will cause it to deflect by stretching to the side having lower pressure and it will return back to center on its own when the pressure is relieved. In contrast, the membrane diaphragm of the Gangemi patent unfolds under pressure, does not have a return force, and requires an external force to return it to its original position. The Gangemi construction increases the risk that the membrane will bottom out in use and transmit inaccurate pressure readings.
Therefore, it is an object of the present invention to provide isolating and blood transmitting apparatus that enables a safe, relatively accurate pressure transmission.
A further object of the present invention is to provide an isolating and blood pressure transmitting device that is simple in construction and is easy to manufacture.
Another object of the present invention is to provide isolating and blood transmitting apparatus that is constructed so as to allow a pair of the devices to be placed adjacent to each other with the respective inlets and outlets being located at only a small distance from each other.
A further object of the present invention is to provide an isolating and blood transmitting apparatus that may be produced readily by injection molding.
A further object of the present invention is to provide isolating and blood transmitting apparatus which uses a generally planar membrane that is centered within a pair of generally hemispherical housing members, with the periphery of the membrane being compressed by the housing whereby greater pressure on either side of the membrane will cause it to deflect to the other side by stretching.
Other objects and advantages of the present invention will become apparent as the description proceeds.